The atmosphere above Llano de Chajnantor
At the APEX site on Llano de Chajnantor the amount of perceptible water vapour (PWV) is typically 1.0 mm and falls below 0.5 mm up to 25% of the time. The image below shows the atmospheric transmission between 200 GHz and 1.6 THz for different PWV values.
In order to prepare the observations and make time estimates for different atmospheric conditions the following atmospheric transmission calculator can be used. It is based on the ATM model written by Juan Pardo. The calculator covers the frequency range 200 to 1600 GHz.calculator
This plot shows the PWV as function of month as measured by the ALMA radiometer.